Please help and explain to me how to solve this

Given:
There is a graph given in the question
Required:
We need to find the approximate cost of year 1987
Explanation:
Here we can see in the graph that
There are two points as
[tex]\begin{gathered} (x_1,y_1)=(1983,5093) \\ (x_2,y_2)=(1991,10027) \end{gathered}[/tex]Now by using midpoint formula
[tex](\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})=(\frac{1983+1991}{2},\frac{5093+10027}{2})=(1987,7560)[/tex]Final answer:
The approximate cost of year 1987 is $7560